tdd

What problem does it solve? Writing tests after the fact or in bulk often produces brittle tests coupled to implementation details that break on every refactor. This Skill enforces a disciplined test-driven development workflow where tests verify observable behavior through public interfaces, so they survive internal changes. ## Core Features & Use Cases - Red-Green-Refactor Loop: Implements vertical slicing with tracer bullets—one test, one minimal implementation, repeated incrementally instead of writing all tests upfront. - Behavior-Focused Testing Guidance: Distinguishes good integration-style tests from bad implementation-coupled tests, with concrete examples of mocking boundaries and interface design. - Reference Material: Includes guidance on deep modules, interface design for testability, when to mock, and post-cycle refactoring candidates. - Use Case: When adding a checkout feature to an e-commerce app, use this Skill to plan which behaviors to test, write one failing test at a time through the public API, and refactor safely once all tests pass. ## Quick Start Use the tdd skill to build the new payment retry feature test-first, one behavior at a time.